This invention is in the field of systems, including devices, implanted within or attached to a human patient, for monitoring biological activity. The invention is preferably applied to the monitoring of cardiac status, providing early detection and/or prediction of unwanted medical conditions and alarming the patient in response thereto.
Implantable devices which monitor and store sensed data and provide alarms when pathological conditions occur will both revolutionize medical care in the near future and also greatly increase our understanding of the physiological and metabolic processes and states that occur in healthy and sick individuals. One obvious area where these devices will have a central role is in the treatment of neurological and cardiac disorders. In the case of cardiac disorders, the ability to monitor, detect, and predict cardiac abnormalities related to, for example, ischemic factors will decrease the fatalities related to these disorders by providing patients with sufficient prior warning to allow them to obtain treatment or intervention prior to having a fatal heart attack. Fischell et al in U.S. Pat. Nos. 6,112,116, 6,272,379, 6,468,263, 6,609,023 and 6,985,771 which are incorporated herein by reference, describe such systems for acute detection and warning, however, these do not provide comprehensively for measuring and storing data related to trends of cardiovascular health over extended periods of time. Other relevant prior art are U.S. Pat. Nos. 6,980,851 6,741,885 and US applications 2005/0177049, 2003/0083582 and 2003/0004548, which describe measurement and storage of cardiac data, and also describe providing alarms in response to detection of abnormal events.
While coronary narrowing or blockage (e.g., atherosclerosis, thrombosis, and stenosis) can be treated by angioplasty and the introduction of cardiac stents, subsequent monitoring, after surgical or other type of intervention, would be useful in order to ensure that the effects of an intervention continue to be sufficient. Further, in interventions such as heart replacement, or implantation of a pacing or defibrillation device, follow-up monitoring can provide an ongoing indication that the procedure is having its intended effects. The monitoring system can provide alarm warnings when sensed data indicate that the intervention has become inadequate to deter abnormal cardiac activity. Monitoring of operations of implanted devices (e.g., amount of drug or stimulation delivered over a specified duration), and biological activity which is time-locked to operations of these implanted devices (e.g., post-stimulation activity), and ongoing endogenous biological activity may all be monitored. For example, an increase in the occurrence of responsive therapy, such a pacing therapy, over time may indicate that the heart is getting sicker or that pacing is losing its efficacy.
Fischell et al. in U.S. Pat. No. 6,272,379 discloses an implantable cardiac monitor that can detect ischemia by evaluating the ST segment of a patient's electrogram. Specifically, the ST segment deviation is compared to a threshold, which may be programmed before and/or after the device is implanted within a patient. It may be desirable to improve upon the algorithms disclosed in the '379 patent.
Fischell et al. in US Patent Application 2005/0113705 describes a cardiotracker system which allows for extended recording of cardiac data by transforming the time-series cardiac data into histograms which summarize the cumulative frequency and distribution of various measures of the electrogram. Trending of data and generation of summary results are also described. The '705 application also discloses alerting for predicted future events based on a combination of a recent trend for a parameter (e.g., the rate of change of a parameter over a prior period) and the current level of the parameter. As such greater rates of change may result in an alert being issued at an earlier time than the occurrence of the future event. The absolute level of a parameter is a function of the rate of change of that parameter.